IICT – geo.SYSIN Towards web services dedicated to thematic mapping Olivier Ertz, Abson Sae-Tang FOSS4G'07, September 2007

Research activities : ● ICT Institute (Switzerland) – network, 3D, e-Content,... ● SYSIN Research Unit : – CMS, LMS, collab. platform,... ● geo.SYSIN Lab : – Geographic e-content Teaching activities : Partnerships : Who, where, what...

FOSS4G2006 : amazing experience as organizers...

Road map of this presentation ● Hot focus of the project ● From primary mapping to thematic mapping ● SLD “Hello world” ● SLD for thematic mapping, examples, problems ● Towards an extension of SLD ( SLD-T ) ● Tracks of implementations ● Conclusions

Hot focus of this project ● Interoperability of geographic web services dedicated to thematic mapping ● Put the emphasis on a web services based architecture in respect of the spatial standards from OGC and graphics ones from W3C. ● Use OGC specifications for web thematic mapping. ● Well, what is web thematic mapping ?

Primary mapping (1) “Boundaries are purple polygons” “Bus stops are yellow points with black outline” “Boat lines are dashed blue lines” “Train lines are in red” How to symbolize features according type Useful to explore the map, it's inventory mapping

Primary mapping (2) symbolize features according category

Then it comes to thematic mapping ● About how to symbolize statistical data that belong to features (like election results, halieutics ressources, census data... ) ● New kind of maps : – Choropleth maps... – Proportional symbols... – Pie charts, histograms... – And many more...

Thematic maps considered Choropleth map Carthema5

Thematic maps considered Proportional symbol (circle, triangle, square,...) Carthema5

Thematic maps considered Bivariate symbols (proportional symbol + choropleth) Carthema5

Thematic maps considered Overlaid symbols (2 proportional symbols) Carthema5

Thematic maps considered Pie chart (and proportional symbols) Carthema5

Thematic maps considered Bar chart (horizontal) Carthema5

Thematic maps considered Juxtaposed symbols Carthema5

How to describe these maps ? ● Can we use SLD ? – OGC Styled Layer Descriptor Implementation Specification is an encoding that extends the Web Map Service specification to allow user-defined symbolization of feature data. – It allows users (or other systems) to determine which features or layers are rendered with which colors or symbols. ● Many FOSS for webmapping are SLD compliant (Geoserver, Deegree...) ● This project is first a study on how far we can go with SLD for thematic mapping

SLD “Hello world” example #ffffaa Yellow # Black

SLD to created thematic maps ● Possible maps – Choropleth – Proportional symbol – Overlaid symbol – Bivariate symbol ● No possible maps – Juxtaposed symbol – Pie chart – Bar chart

SLD - Proportional symbol circle #6688aa Blue # Black YES_EEE_92 YES votes for the adhesion into the EEE in 1992

SLD - Choropleth map From 10 to 50 Density #00ff00 Green One for each category (class) Filter criteria have to be specified for each rule -> redundancy

SLD - Bivariate symbol rule 1... Same as choropleth before... Same as proportional symbol before #00ff00 Green... Same as proportional symbol before One for each category Filter criteria, shape and size symbol have to be specified for each rule -> redundancy YES votes for the adhesion into the EEE in 1992 classified by canton

SLD - Overlaid symbol... YES_ONU_02... YES_ONU_86 Even if blue value is smaller than the orange one, it is always drawn first ! -> no priority according value in the render process ! Possible solution : use to determinate witch symbol have to drawn first.

SLD - Overlaid symbol YES_ONU_86 YES_ONU_02... YES_ONU_86 YES_ONU_02... Repeat two times almost the same ! -> Redundancy

SLD xlink for Pie chart Name Vaud <OnlineRessource xmlns:xlink=" xlink:type="simple" xlink:href="Vaud.png"/> image/png One and one image for each district (167) ! Need to be able to produce all the images to put on the map -> symbol server

SLD 1.1 and GML – Bar chart ● Create a new Layer ● Use to define features (bars) in GML ● Styling the features created – GML is for geographical data not graphics !!!

SLD 1.1 and GML graphics for Bar chart Define the bar coordinate with GML here... One polygon per district (167) Define the bar coordinate with GML here... One polygon per district (167) ONUVote Fill bar in green ONUVote Fill bar in red Too verbose !

Towards an extension of SLD ● Problems with current SLD : – SLD is thematic mapping capable, but complicated ways to describe some thematic maps and limits ● Verbose, redundant... ● Rendering order according value... ● Symbolizer (point) can not be moved (multisymbol) ● Solution – Specify thematic mapping concepts into an extension of SLD (SLD-T for Thematic) – Introduce specific terminology of thematic mapping world

How to extend SLD ● New symbolizer like PointSymbolizer, TextSymbolizer, etc... -> ThematicSymbolizer ● Insert in the Rule element as a child of sld:Symbolizer

ThematicSymbolizer ● Abstract element such as sld:Symbolizer ● Common element to all thematic symbolizer Juxtaposed symbol Symbol priority inside one Rule Text to drawn with the symbol Pie chart, bar chart Proportional symbol Choropleth, bivariate Overlaid, juxtaposed

SLD-T for overlaid symbols SLD... circle... -YES_ONU_ YES_ONU_02...

SLD-T for juxtaposed symbol Right placement Left placement

SLD-T for choropleth map... Common class styling Filter criteria described one time or UniqueValueCategory One category for each class to symbolize. A DefaultCategory could be specified Density

SLD-T for pie chart VOTES Like Mark from PointSymbolizer ~ BaseSymbolizer Pie chart, bar chart ? All pie slice Non vote slice To determinate the value in percent. Here it is already in percent Pie YES_ONU_02 Fill in green Fill in red Chart size

Tracks of implementations ● Extend a current implementation like Geotools – Just a start to see something on screen ● Create our own implementation : – Perhaps with IRSTV Lab in Nantes (France) ● SLD-T editor and renderer for OrbisGIS – Using a thematic symbol server ● SLD-T = SLD + xlink to external images ● Still some redundancy – Explore opportunities of implementations, case studies with our partners...

Conclusion and questions... ● SLD-T covers all thematic maps (flow maps?) ● Complete implementation still to be done ● SLD-T introduces thematic mapping specific terminology (human-readable descriptor) ● Interesting steps for SDI projects wanting to publish thematic maps ● No link with OGC ● Stay aware of SLD evolutions, KML styling...

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